The primary goal is to perform pediatric clinical studies to identify a live attenuated vaccine against RSV. We also have performed or are performing clinical studies for HPIV1, HPIV2, HPIV3, and HMPV candidates. In the future, studies with the HPIVs will be restricted to strains that also express RSV antigen as bivalent vaccines. All vaccine viruses are developed and produced from cloned cDNAs using reverse genetic systems of our making and employ defined attenuating mutations of our making. We develop candidates in pre-clinical studies and prepare vaccine seeds. Vaccine manufacture is performed under contact under our supervision, and clinical evaluation is performed by contract or collaboration under our supervision. Vaccines are evaluated clinically beginning in adults (who are seropositive for these common viruses), and moving successively to seropositive older children (typically 12-59 months of age) followed by seronegative younger children and infants (typically 6 -24 months of age for RSV, 6-59 months of age for the others). For RSV and HPIV3, viruses may be evaluated further in virus-naive young infants 1-3 months of age. Adult studies are open-label, whereas pediatric studies are double-blind placebo-controlled with a 2:1 ratio of vaccine to placebo recipients. For all RSV studies, subjects are followed during the subsequent RSV season (Nov 01 to March 31) following the experimental immunization in order to assess the longevity of the antibody response and the rate and severity of natural RSV infection (although these studies are too small to reliably assess protective efficacy), and to confirm the absence of enhanced RSV disease. RSV vaccine: We previously made an RSV vaccine candidate called RSV delM2-2 that is based on deletion of most of the ORF encoding the M2-2 protein. This mutation down-regulated viral RNA replication and up-regulated viral gene transcription and antigen synthesis, raising the possibility of increased immunogenicity. In addition, deletion of an ORF should be refractory to reversion or compensation, providing increased genetic and phenotypic stability. We performed a phase 1 clinical study (NCT01459198) of a version of this mutant whose seed virus was supplied by MedImmune and is called RSV MEDI delM2-2. In seronegative children, and compared to our previous lead RSV vaccine candidate rA2cp248/404/1030delSH, the delM2-2- virus was significantly more restricted for shedding in nasal washes but induced significantly higher titers of RSV neutralizing serum antibodies. Thus, it indeed appeared to have increased immunogenicity per infectious unit. In this particular trial, there was an unusually high incidence of adventitious infections by other respiratory viruses in both the vaccine and the placebo groups, which confounded evaluation of tolerability. Surveillance during the subsequent RSV season showed that several RSV MEDI&#8710;M2-2 recipients had substantial antibody rises without reported illness, suggesting that the vaccine was protective yet primed for anamnestic responses to RSV. Rational design appears to have yielded a candidate RSV vaccine that is intrinsically superior at eliciting protective antibodies in RSV-nave children, and highlights a new approach for the development of live-attenuated RSV vaccines. We presently are conducting a second phase 1 study in 51 additional seronegative children 6-24 months of age (NCT02040831). This study involves a version of the delM2-2 virus that was derived in our laboratory and is called RSV LID delM2-2. Part of this study is being done in collaboration with the International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) Group. The rA2cp248/404/1030delSH virus mentioned above contains a series of point mutations and deletion of the SH gene, and is highly temperature-sensitive, but exhibits genetic instability involving at least two attenuating mutations. We previously developed a new version of this virus, called cps2, in which these two mutations have been modified for increased genetic stability. RSV cps2 is presently in a phase 1 study in seronegative children 6-24 months of age (NCT01852266). This study involves 51 subjects, and part of this study is being done with IMPAACT. We also previously developed another RSV vaccine candidate called RSV delNS2del1313. This virus contains the deletion of the nonstructural protein-2 (NS2) gene, which encodes a protein that antagonizes host responses to viral infection, notably the type I interferon (IFN) response. It also contains deletion of codon 1313 in the polymerase L protein. This virus presently is being evaluated in a phase 1 study in 30 seronegative children 6-24 months of age (NCT01893554). Thus, we have three promising RSV platforms in phase 1 studies: RSV delM2-2, RSV cps2, and RSV delNS2del1313. These viruses have different properties (such as temperature-sensitivity and differences in antigen expression) and different mechanisms of attenuation (involving effects on RNA synthesis, regulation of RNA synthesis, IFN antagonism, among others). Our goal is to expeditiously identify a suitable live attenuated RSV candidate to bring forward into larger studies. The RSV delM2-2 virus appears to be particularly promising. Wild type (WT) RSV: We prepared a clinical trial lot of WT RSV strain A2 produced from cDNA. This provides a virus with a well-defined passage history and reduced possibility of adventitious agents. This virus will be evaluated for infectivity, replication, pathogenesis, and immunogenicity in adult volunteers. This will provide an infection model that can be used to evaluate antiviral drug candidates and vaccine candidates, and to study viral pathogenesis and the host response. HPIV3 vaccine: We previously developed and evaluated an attenuated version of HPIV3 called rHPIV3 cp45. This is a recombinant version of a biologically derived cold-passaged (cp) virus that we previously showed has satisfactory infectivity, safety, immunogenicity, and lack of transmissibility in seronegative infants and children in phase 1 and 2 studies. LID re-derived this virus from cDNA to provide a known pedigree for safety reasons. This virus was indistinguishable from its biological parent in a phase 1 study in seronegative infants and children, and thus is available to take to larger studies and combine with an RSV candidate when the optimal candidate is identified. We previously evaluated a combination of HPIV3 cp45 plus an attenuated RSV strain in a phase 1 study in seronegative children and showed that the two viruses were compatible, and that the bivalent vaccine was well-tolerated and immunogenic. A second HPIV3 vaccine based on bovine PIV3 in which the F and HN genes were replaced with their counterparts from HPIV3 also has been evaluated in seronegative infants and children and was attenuated, well-tolerated, and immunogenic. HPIV1 vaccine: We previously developed an HPIV1 vaccine candidate called rHPIV1-C(R84G/del170)HN(T553A)L(Y942A) that includes mutations that were engineered for genetic stability. A phase 1 study in seronegative children 6 to 59 months of age (NCT00641017) showed that this virus is over-attenuated. Over-attenuation can be corrected by reverse genetics. HPIV2 vaccine: We previously developed an HPIV2 vaccine candidate called rHPIV2-V94(15C)/948L/1724 that includes stabilized mutations. This virus presently is being evaluated in a phase 1 study in seropositive children 15 to 59 months of age (NCT01139437). HMPV vaccine: We previously developed an HMPV vaccine virus called rHMPV-Pa in which the HMPV P gene was replaced by that of avian MPV, thus conferring a host range attenuation phenotype. This virus is presently being evaluated in a phase 1 study in seronegative children 6-59 months of age (NCT01255410).